The extent to which a greater proportion of small behavior changes could be detected with momentary time-sampling (MTS) was evaluated by (a) combining various interval sizes of partial-interval recording (PIR) with 20 s, 30 s, 1 min MTS and (b) using variable interval sizes of MTS that were based on means of 20 s and 1 min. For each targeted percentage, low, moderate, and high inter-response times (IRTs) to event-run ratios were compared with reversal designs to determine whether sensitivity increased with either variation of MTS. The results showed that (a) combinations of 30 s and 1 min MTS/PIR yielded increased sensitivity over MTS alone; however, the increased sensitivity was offset by an increased probability of generating false positives and (b) variable-interval MTS produced comparable sensitivity to fixed-interval MTS. Thus, none of the methods increased detection of small behavior changes (decreased false negatives) without also increasing false positives. Copyright © 2009 John Wiley & Sons, Ltd.